OSWIECIM, Poland — More than 3,000 guests, including Holocaust survivors and foreign dignitaries, gathered on Tuesday at a site marking one of history’s biggest horrors, the Auschwitz-Birkenau death camps in Poland, which were liberated by Soviet troops 70 years ago in the closing months of World War II.

Because of the survivors’ advancing age, this year’s ceremony at the Auschwitz-Birkenau State Museum may be the last major anniversary celebration to include more than a handful of people who endured the Nazi camps here, where about 1.5 million people lost their lives, most of them European Jews. Some 1,500 survivors attended the 60th anniversary in 2005, but on Tuesday there were fewer than 300 on hand. Most are in their 90s, and some are older than 100.

Their dwindling numbers prompted many at the ceremony to raise the question of how best to sustain memories of the horror when they are gone, and what it means in a time of fresh outbreaks of religious and ethnic animosities.

“Today, in the name of truth, we need to fight the attempts to relativize the Shoah,” President Bronislaw Komorowski of Poland said as he opened the ceremony, using another term for the Holocaust. “The memory of Auschwitz means the memory of the importance of freedom, justice, tolerance and respect for human rights,” he added.

Dozens of heads of state and other prominent figures took part in the ceremony, including the presidents of France, Germany and Austria, François Hollande, Joachim Gauck and Heinz Fischer; the kings of Belgium and the Netherlands, Philippe and Willem-Alexander; and Crown Prince Frederik of Denmark. Treasury Secretary Jack Lew represented the United States, while Russia was represented by Sergei Ivanov, President Vladimir V. Putin’s chief of staff.

The anniversary takes place at a time when reports of anti-Semitism are increasing across Europe. One Jewish organization said in a recent report that the incidence of anti-Semitic acts in France had doubled over the past year.

“Jews are targeted in Europe once again because they are Jews,” Ronald S. Lauder, president of the World Jewish Congress and a major contributor to the preservation of the museum complex, said at the ceremony.

Mr. Lauder, 70, said the recent terrorist attacks in Paris, including one at a kosher supermarket, had prompted him to radically change the remarks he intended to deliver. He called on the world leaders in the audience to adopt policies of zero tolerance toward hatred of any kind. “Unless this is checked right now, it will be too late,” he said.

Steven Spielberg, whose Holocaust film “Schindler’s List” won seven Academy Awards, raised a similar warning in a short speech on the eve of the anniversary, saying that Jews were once again threatened by “the perennial demons of intolerance.”

Speaking at a Shoah memorial in Paris before flying to Poland for the ceremony at the museum, Mr. Hollande pleaded with Jews in his country not to react by emigrating. “The place of Jews is in France,” he said. “France is your homeland.” He called on Internet service providers to take action against anti-Semitic comments posted online.

Mr. Gauck also gave a speech at home before traveling to Poland. He told a commemorative session of the German Parliament that “while the Holocaust will not necessarily be among the central components of German identity for everyone in our country, it will still hold true that there is no German identity without Auschwitz.”

He spoke of the difficulty many Germans had over the years in acknowledging what had happened during the war. “Remembering the Holocaust remains a matter for every citizen of Germany,” Mr. Gauck said. “It is part and parcel of our country’s history.”

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Survivors and families carried candles as they visited a memorial at the Birkenau camp.CreditSean Gallup/Getty Images

For the first time, the memorial ceremony here was sheltered from the January weather, under a tent large enough to enclose the entire red brick gateway to the Auschwitz II camp, for many a symbol of the Nazi atrocities. Several survivors were among the speakers.

“The greatest debt we have today is to pass on the memory of their lives to others, their desire and will to live,” Halina Birenbaum, who was at Auschwitz-Birkenau as a child, said of those who were killed at the camps. “Only in my memories, I can be with my loved ones who died here. Only in my memories, I can recognize right from wrong.”

“People forget what Auschwitz was,” Ms. Birenbaum said, “and that terrifies me, because I know to what kind of hell it leads.”

Administrators of the museum, which includes the remaining grounds of the Auschwitz and Birkenau death camps, said that the museum’s mission, once focused primarily on survivors, was evolving toward memorializing the Nazi atrocities for generations born after the war.

Roman Kent, chairman of the American Gathering of Jewish Holocaust Survivors and Their Descendants, was a teenager when he was imprisoned in Auschwitz. As he spoke on Tuesday, he struggled to keep his emotions in check.

“How can I forget the smell of burning flesh that constantly filled the air?” he said in a trembling voice as tears rolled down his cheeks. “Or the heartbreak of children torn from their mothers? Those shouts of terror will ring in my ears until I am laid to rest.”

The ceremony concluded with the survivors, who were awarded medals, and the assembled dignitaries placing candles in remembrance of Holocaust victims, arranged symbolically in a straight row that was called “a line under history.”

Correction:Jan. 29, 2015

Because of an editing error, an article on Wednesday about a ceremony in Poland marking the 70th anniversary of the liberation of the Auschwitz-Birkenau death camps at the end of World War II referred incorrectly to one survivor at the ceremony. The survivor, Halina Birenbaum, is a woman. Because of other editing errors, two accompanying picture captions misstated the day of the anniversary events. As the article correctly noted, they took place on Tuesday, not on Wednesday.

Alison Smale contributed reporting from Berlin.

A version of this article appears in print on , Section A, Page 4 of the New York edition with the headline: Outliving Horror for 70 Years and Never Forgetting. Order Reprints | Today’s Paper | Subscribe